SweetPea & Euro Traveler,
I have experienced the same issue as well. At first I didn't but I have seen it twice now and I don't have a SD card. Both times happened when I added a few large about 5MB and it didn't go into screen saver. So it has something to do with not being in screen saver or when you add the books, and it possibly indexes them. From what I read the device uses no power when displaying the screen, only turning pages.